Herbicide Resistant Weeds

Negative cross-resistance in triazine-resistant biotypes of Echinochloa crus-galli and Conyza canadensis.

Gadamski, G., D. Ciarka, J. Gressel, and S. Gawronski W. 2000. Negative cross-resistance in triazine-resistant biotypes of Echinochloa crus-galli and Conyza canadensis. Weed Science. 48: 176-180.

Whole-plant, negative cross-resistance was studied in Conyza canadensis and Echinochloa crus-galli, important global weeds. Negative cross-resistance can be a most useful preemptive, cost- effective tool for delaying the evolution of resistance, as well as for resistance management, after resistant populations evolve. Seeds of triazine-resistant and -susceptible biotypes were collected in or near orchards in Poland that had been continuously treated with atrazine for more than 10 yr. Plants grown from the seeds were treated, in a greenhouse, with herbicides from the following chemical families: triazine, benzothiadiazole, phenyl-pyridazine, arylophenoxypropionate, cyclohexanedione, phenoxycarboxylic acid, pyridine carboxylic acid, phosphinic acid, glycine phosphate, chloroacetamide, sulfonylurea, and bipyridylium. Eleven of the 18 herbicides tested exerted significant negative cross-resistance against atrazine-resistant weeds, ranging from 0.03 to 0.67 of the concentration required to affect the triazine-sensitive type. No synergism was found between bentazone and fluroxypyr in mixture on Conyza, even though both separately exerted negative cross- resistance. Using a mixture with half the amount of each component lowers the environmental effect of each component while controlling a broader spectrum of other weeds.